Use the "Search" button in the forum, and you should be able to find the article regarding this issue. It happens before, and I believe it's Apple's design flaw. Call Apple Care and they should be able to replace that for you free of charge.
Sorry for the English input, I don't have Chinese input installed on my work computer.
But it is in the AppleCare coverage here in Brazil. Which means free repairing and free new keyboard. You'll have to take your macbook to an authorized service provider and it will take about a few days for them to change the upper case.